Replies

1. 
   ErnieConover | Sep 02, 2006 03:21pm | #1

   Your best internet source would be McMaster Carr. Their URL is http://www.mcmaster.com/. Once on the start page type O1 Steel into the search engine and you will be offered an array of tool steel in 18 and 26" lengths. O1 (pronounced oh one) is a superior oil hardening tool steel that is perfect for making small tools. It is sold annealed and you will have to harden it which can be done with a MAPP gas torch. Draw it to pale straw yellow which is about 60 Rockwell C Scale. If you need directions on heat treating let me know.

   With best regards,
   Ernie Conover

1. 
   M1 | Sep 02, 2006 05:19pm | #2

   Hi Mr. Conover,

   Thank you very much for your reply.

   I would like very much to receive further instructions on tempering the O1 steel blank with MAPP gas.

   I look forward to your reply.

   Again, thank you very much.

   Sincerely,

   M1

1. 
   ErnieConover | Sep 02, 2006 06:27pm | #3

   Once you have shaped your iron to the desired shape heat the cutting edge, and as far behind it as you can, to a bright cherry red color. Once bright cherry (it should be sparking a bit) quench the tool by plunging it into oil. Although you can use kerosene motor oil is better for its lower flash point. There is the posibility of a fire so wear a glove and do it in an appropiate spot. Although the quenching process seems rather casual it is very important that it be done in such a way that steam pockets do not build up around the work for steam insulates heat transfer creating soft spots. After quenching the steel is as hard as it can get, depending on the carbon content. With 1% or more of carbon this should be 60 to 65 degrees Rockwell C. Your O1 will be this hard.In fact such a steel would be so hard that it would lack toughness and be like a frozen turkey when dropped. Therefore the next task is tempering the tool by drawing back some of the hardness to a good compromise between hardness and toughness. To temper first polish the tool to a bright finish. Now slowly and evenly heat it with the torch watching carefully. (It is best to heat an inch or so behind the cutting edge and let the heat run to the edge so as not to overheat this area. More about this below.) Carbon steels turn specific colors at specific temperatures. As a rule of thumb edge tools such as knives and chisels are drawn to pale straw-yellow to deep straw-yellow which is between 58 to 60 degrees Rockwell. Other tools such as axes, auger bits, and cabinet scrapers needed more toughness so are drawn back to bright blue which is around Rockwell C 45.This same blue is responsible for the blue color of clock springs. In fact a blue temper is often called spring temper. One advantage to "tempering by eye" is that on a tool with a thin edge, such as a skew chisel, the heat can be applied to the shank in back of the edge. The heat is allowed to travel up to the edge. If the edge is pale straw-yellow or deep straw-yellow the shank is generally bright or even light blue. The advantage is that the tool has hardness at the edge with toughness in the shank - a good combination. Traditionally tools were made from water hardening steel with the only alloying ingredient being carbon. The problem with a water quench is that it is very severe and warpage, distortion and even cracking can occur. It is not uncommon for something like a flat scraper blank to come out of the forge nice and straight and come out of the quench bowed. Sharp inside corners are avoided with tools made from water quenching steels, because cracks due to stress build up often form at such places. Actually though, good tool design dictates avoiding sharp corners, especially inside corners, as they are natural focal points for stress.For the steel structure to change from soft to hard the rate of cooling during quench is critical. Every alloy of steel has a critical rate of cooling. Unless cooled at the critical rate, or faster, annealing rather than cooling will occur. Plain high carbon steels need the severity of a water quench. Brine is even used sometimes, because salt water adsorbs heat even faster. Metallurgists working in the first half of this century; therefore, came up with oil and air quenching steels to avoid such problems. By alloying manganese into the steel the critical rate of cooling is slowed and oil rather than water quenching can be used. O in O1 stands for oil and this is the steel you are using. Today we even have steels which can be air quenched by simply placing them in front of a fan in moving air. Such high speed steels make possible the high precision parts of our space age. Quenches in their order of severity are brine, water, oil and air respectively. Air quenching can only be done effectively in special furnaces or severe oxidation will occure.With best regards,
   Ernie Conover

1. 
   M1 | Sep 03, 2006 07:14pm | #4

   Hi Mr. Conover,

   I wanted to let you know how much I appreciated the in-depth instructions on tempering the plane tool steel blanks.

   Thank you so very much.

   Best Regards,

   M1

2. 
   JohnWW | Sep 27, 2006 05:16pm | #5

   Ernie,

   Beautifully written, probably the best short explanation I've read about hardening and tempering steel.

   John White, Fine Woodworking Magazine

    

1. 
   ErnieConover | Sep 27, 2006 06:38pm | #6

   Dear John,Thanks for the kind words. It is a special compliment knowing your proficiency in this area.With best regards,
   Ernie Conover

2. 
   Joe Sullivan | Apr 10, 2007 09:32pm | #7

   Ernie:

   Now that I have found this piece -- and I agree with John White, BTW, it raises a couple of questions that started above.  First, with older steels of unknown composition, say, old socket chisels or turning chisels:

   a) how do you test to see if they require heat treatment;

   b) what quench would be advisable?

   And a related question:  If a drill bit goes blue at the tip, I assume it has lost temper. Can I reharden it using this method?

   Oh, just one more thing -- we have an old portable forge.  Have not done much with it except for my son making a couple of knives.  Is there a reason NOT to use the forge for this process instead of a torch?

   You know, I should have hung around the lab more back when I worked in a steel foundary.

   Cheers, and many thanks

   Joe

   Edited 4/10/2007 2:33 pm ET by Joe Sullivan

   Edited 4/10/2007 2:36 pm ET by Joe Sullivan